1. Field of the Invention
The present invention relates to image analysis methods for determining the exterior points of an object in a background. The present invention also relates to a a method for identifying at least one valid object having at least one valid object predetermined attribute value in a background using automatically calculated thresholds by using the methods for determining the exterior points of the object.
2. Description of the Related Art
The ability to access interior points of a region when its contour is given is a classic problem in image processing. Previous solutions to this problem have been described by L. W. Chang and K. L. Leu in an article entitled "A Fast Algorithm for the Restoration of Images Based on Chain Codes Description and Its Applications", Computer Vision, Graphics, and Image Processing 50, 296-307 (1990). One algorithm described, connectivity filling, requires that every pixel in the object be interrogated. Since the number of pixels within an object is greater than the number of pixels which comprise the perimeter of the object, such a technique is relatively slow. Another method described is parity checking which is based on the fact that the intersection of a straight line with the contour regions of an object delineates an even number of points on the perimeter of the object. Designation of the interior points is determined by an arbitrary filling rule where all points between each odd point and the next even point on the contour in each line of the image are designated as interior points. Such a parity checking algorithm will not work with objects of complex shape.
The the same article cited above, Chang and Leu propose an enhanced parity checking algorithm which relies on characterizing the perimeter points into one of four categories based on direction code values. Characterizing the points leads to the creation of a new buffer of perimeter points wherein some points have been duplicated and others eliminated. By applying the parity checking algorithm to the newly created buffer, interior points of objects with complex shapes may be identified.
U.S. Pat. No. 5,029,106 to Kai discloses.a pattern data generating system for generating pattern data in which an arbitrary closed graphic pattern whose boundary data is defined on a two-dimensional bit map is filled. Kai examines all the points of the pattern to determine the interior points of the pattern. Kai does not deal with determining exterior points of the pattern.
Japanese Patent Publication Number 62-60069 to Hitachi Electronic Engineering Co. Ltd., published Dec. 14 1987, discloses a colony screening device which distinguishes colonies based on color. Colonies are identified by pattern recognition using a predetermined threshold and a small number of points in the center of a colony are arbitrarily selected. U.S. Pat. No. 4,453,266 to Bacus discloses a method for measuring the optical density of a cell using the sum of gray level values within the closed boundaries of the cell.
None of these references discloses a method for determining the exterior points of an object. Furthermore, none of these references discloses a method of identifying at least one valid object having at least one valid object predetermined attribute value in a background using automatically calculated thresholds by determining the exterior points of the object.